General Calendar Sharing information:

The combination of the user’s sharing permissions and the calendar auto-accept setting will determine the behavior of how an invitation is handled for a resource or user-created calendar.

The sharing options (permissions) are setup by the calendar's owner, for other users with rights to the calendar. 

Here’s what people can do, using each sharing permissions option:

Permission: Make changes AND manage to share

• Change sharing settings
• Add and edit events
• See details for all events, including private ones
• See the time zone setting for the calendar
• Permanently delete the calendar
• Restore or permanently delete events from the calendar’s Trash
  

NOTE: This permission level must be given to a calendar manager, for any Google Resource Calendars (rooms, spaces, etc)

Permission: Make changes to events

• Add and edit events
• See details for all events, including private ones
• See the time zone setting for the calendar
• Restore or permanently delete events from the calendar’s Trash

Permission: See all event details

• See details for all events except those marked as private
• See the time zone setting for the calendar

Permission: See free/busy information (no details)

• See when your calendar is booked and when it has free time, but not the names or other details of your events.

User's Personal Calendar Sharing Information:

For a user's personal primary calendar, and for any additional calendars they create, see the Google Article about sharing your calendar.

Share your calendar with someone